Lab Test

Ethosuximide Level


Test Codes

Warde: ETHSX, EPIC: LAB5389, Beaker: XETHO

Specimen Collection Criteria

Collect: One plain Red-top tube. (Minimum Whole Blood: 2.0 mL)
Acceptable: Plasma, Lavendar EDTA, Green Sodium or Lithium Heparin.

Do not use Serum Separator Tubes.
Time of Collection:
Trough, just prior to the next dose.
Record the exact time of specimen collection on the tube or in the computer system.

Physician Office/Draw Specimen Preparation

Let specimens clot 30-60 minutes. Refrigerate (2-8°C or 36-46°F) the collection tube within two hours of collection. (Minimum: 0.2 mL blood)

Preparation for Courier Transport

Transport: Collection tube, refrigerated (2-8°C or 36-46°F). (Minimum: 0.2 mL blood)

Rejection Criteria

  • Serum Separator (SST) tubes.
  • Severely lipemic or hemolyzed specimens.

In-Lab Processing

Let specimens clot 30-60 minutes. Centrifuge specimen to separate serum from cells. Deliver an aliquot of serum or the collection tube immediately to the appropriate testing station.


Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): 48 hours
Refrigerated (2-8°C or 36-46°F): 14 days
Frozen (-20°C/-4°F or below): 14 months


Warde Medical Laboratory


Monday – Friday.
Results available 1-3 days.

Reference Range

Therapeutic Range: 40-100 mcg/mL.
Critical: > 200 mcg/mL.

Test Methodology

High Performance Liquid Chromatography.


Ethosuximide has an elimination half-life of from 1 to 3 days. Up to two weeks may be required to achieve steady-state. Drugs that induce oxidative metabolism will typically increase Ethosuximide clearance.

Clinical Utility

This assay is used to monitor the therapeutic drug concentration and evaluate the toxicity of ethosuximide. Ethosuximide is an anticonvulsant that is the drug of choice in the treatment of absence (petit mal) epilepsy.

CPT Codes

LOINC: 3616-0, Last Dose Date  29742-4, Last Dose Time  29637-6


Last Updated


Microtainer® and Vacutainer® are registered trademarks of Becton, Dickinson and Company.
UroVysion® is a registered trademark of Abbott Laboratories. ThinPrep® is a registered trademark of Hologic, Incorporated.